1. Field of the Invention
The present invention relates to an optical transmission line used for a long distance communication. Particularly, it relates to an optical transmission line enabling definition of a fault point and a method for defining (or, locating) the fault point on the optical transmission line. The fault point can be found by detecting discontinuous points on a curve of the relationship between the intensity of a reflected light on the optical transmission line and the distance from an end of the line to each discontinuous point. In general, the discontinuous points are caused by change in the power of the back-scattered light based on change in the parameters of the optical fibers which form the optical transmission line, as explained in detail below.
2. Description of the Related Art
In long distance communication, such as submarine cables, an optical fiber cable is usually utilized as a transmission line, and various data are transmitted in the form of light signals.
When a fault occurs in the optical fiber cable, it is necessary to detect (define) the fault point without removing the cable from the sea bed. Accordingly, as a general method, the distance from an end of the optical fiber cable to a predetermined point is sequentially measured in order to detect change of the intensity of the reflected light so that it is possible to define the distance from the end of the transmission line to the fault point.
In this method, it is necessary to measure the precise distance from the end of the transmission line to the fault point in order to define the exact fault point.